1. Field of the Invention
The present invention relates to a video signal reproducing apparatus, and more particularly is directed to an apparatus for reproducing video signals recorded on a tape in a manner such that slow-motion reproduction can be carried out without guard-band noise.
2. Description of the Prior Art
In a helical scan type video recording and reproducing apparatus, video signals are successively recorded by two rotating heads on a magnetic tape in record tracks extending obliquely with respect to the longitudinal direction of the tape. Usually, the two rotating heads have different azimuth angles to achieve high density recording, in which adjacent tracks of the tape are in an abutting or partially overlapping relation to each other. In this regard, cross-talk signals from adjacent tracks can be effectively reduced as a result of azimuth loss of the heads.
For slow motion reproduction of these recorded video signals, the tape is driven at a speed which is slower than that used in the recording mode (or normal reproducing mode). Accordingly, during reproduction, the rotating heads repeatedly trace the respective tracks a number of times, whereby the reproduced picture has a slower motion than it would have if reproduced in a normal reproducing mode. In this manner slow-motion reproduction is achieved. Moreover, when the tape is stopped, a single track is repeatedly traced by the rotating heads to reproduce a still picture.
In the slow-motion reproducing mode or the still picture reproducing mode, the rotating heads rotate at the same speed as in the normal reproduction mode, while the tape is driven at a speed slower than that in the normal reproducing mode or is even stopped completely. As a result, the inclination angle of the track traced by the rotating head on the tape in the slow-motion and still picture reproduction modes differs from the inclination angle of the track in the recording mode (or normal reproducing mode), and this difference in inclination gives rise to tracking deviation.
During reproduction, when one of the rotating heads having one azimuth angle deviates from the track to be scanned and crosses an adjacent track which has been recorded by other rotating head having another azimuth angle, a noise bar is generated in the reproduced picture.
In order to overcome the above-described disadvantage, an improved system, has been proposed as described in U.S. Pat. No. 4,190,869, in which the tape is intermittently driven or shifted by controlling a motor to intermittently drive a capstan. When movement of the tape is stopped, the same tracks are scanned a number of times by the rotating heads each having an azimuth angle corresponding to the track to be scanned, whereby still reproduction is achieved. On the other hand, when the tape is moved at normal speed, normal reproduction is carried out by the rotating heads. Thus, slow-motion reproduction is performed as a combination of still and normal reproduction. It should be noted that the number of fields reproduced from the same track during the still reproduction part of the operation depends on the slow-motion speed.
With the above apparatus, even if one of the rotating heads having one azimuth angle does not cross the adjacent or wrong track recorded by the other rotating head having a different azimuth angle, the one rotating head sometimes traces a large portion of the adjacent or wrong track because of the inclination difference between the record track angle and the head scanning angle. This results in a reduction of the reproduced signal level, causing a lowering of the signal to noise ratio of the reproduced signal and a consequent deterioration of the reproduced picture.